refstring: add GEqualFunc for ref-counted strings

This is the same as g_str_equal() except that it will first check the
string length for equality before dereferencing string contents.

glib/grefstring.c

@@ -234,3 +234,26 @@ g_ref_string_length (char *str)
 
   return g_atomic_rc_box_get_size (str) - 1;
 }
+
+/**
+ * g_ref_string_equal:
+ * @str1: a reference counted string
+ * @str2: a reference counted string
+ *
+ * Compares two ref-counted strings for byte-by-byte equality
+ * and returns `TRUE` if they are equal. It can be passed to
+ * `g_hash_table_new()` as the `@key_equal_func` parameter.
+ *
+ * Returns: `TRUE` if the strings are equal, otherwise `FALSE`
+ *
+ * Since: 2.82
+ */
+gboolean
+g_ref_string_equal (char *str1,
+                    char *str2)
+{
+  if (g_atomic_rc_box_get_size (str1) != g_atomic_rc_box_get_size (str2))
+    return FALSE;
+
+  return strcmp (str1, str2) == 0;
+}

glib/grefstring.h

@@ -56,4 +56,8 @@ gsize   g_ref_string_length     (char       *str);
  */
 typedef char GRefString;
 
+GLIB_AVAILABLE_IN_2_82
+gboolean g_ref_string_equal (char *str1,
+                             char *str2);
+
 G_END_DECLS